The present invention is related generally to the detection of threats to a target using active laser technologies, and more particularly, to an active laser system and method of identifying and classifying an object in a laser beam illuminated scene based on material types.
Mobile military forces can operate in a wide range of environments. These environments can be varied in material types such as naturally occurring sand and vegetation to snow; urban areas with vehicles and buildings; or mountainous terrain. In all cases, man-made or naturally occurring materials radiate reflected and emitted energy based on internal and external sources. Hot objects, for example, radiate heat, a process that can be exploited by passive thermal imagers to discriminate against a cooler background. However, this detection is merely an indication of a thermal gradient. No information is necessarily available on the type of thermal gradient detected.
Primary threats from military adversaries are well understood and developed. Today, the threats to mobile military forces have been reduced to perimeter zones that currently are not served by radar, passive IR sensing systems, or visual identification. Even the most sophisticated passive IR sensors and active radar cannot automatically classify a wide range of targets or such a diverse area as described herein. Current unattended sensors have notoriously high false alarm rates due to the inability to capture enough information necessary to make an intelligent decision. With today's technology, sensing systems might falsely identify a dog as a threat, wasting valuable time and attention.
Passive multi-spectral sensing systems rely on reflected sunlight to view given areas of land. Such systems have been used on space based geographic (LANDSAT, SPOT) and weather satellites (NIMBUS, GOES), for example. Typically, the reflected sunlight is received from the land and passed through a series of band pass filters or a filter wheel to look at radiance at a specific wavelengths. This detection scheme is limited to discrete spectral bands and prescribed by the filter transmission bands. Further, since these passive systems rely on reflected sunlight, the presence of clouds and infrared thermal emissivity can affect and alter the passively collected energy. As such, sophisticated calibration schemes and ground truthing are required to properly determine the scene radiance for the given area of land.
Similarly, there have been extensions to this basic passive multi-spectral sensing technology. One such extension operates through use of a Michelson Interferometer to decompose the reflected sunlight into thousands of channels. This extension is commonly referred to as hyperspectral sensing and employs thousands of spectral channels deconvoluted from the interferometric data using intensive data processing techniques. As with the basic technology, the hyperspectral sensing approach also requires extensive calibration and is often not well suited for battlefield environments.
To overcome the drawbacks of today's sensing systems that include video, infrared imaging, and passive multi-spectral and hyper-spectral sensing, for example, an active laser system for detecting threats around a perimeter of a target has been disclosed in the co-pending U.S. patent application Ser. No. 10/440,918, filed May 19, 2003, and entitled “Laser Perimeter Awareness System” which is assigned to the same assignee as the instant application. This laser perimeter awareness system (LPAS) is based on core technologies of a laser object awareness system (LOAS) disclosed in the U.S. Pat. No. 6,542,227, issued Apr. 1, 2003, which is also assigned to the same assignee as the instant application. Both of the aforementioned documents are hereby incorporated by reference in their entirety into the instant application for providing more structural and operational details of such systems which may not be afforded by the instant application.
Both LPAS and LOAS use a single channel, scanning, eye-safe laser operating at a wavelength of approximately 1.55 microns. The LOAS was developed primarily to enable helicopters and unmanned aircraft vehicles (UAVs) to detect and avoid power lines and other ground structures. The LPAS, which is a variant of the LOAS, is capable of detecting and isolating swimmers in the water, moving vehicles, and persons at ranges spanning several meters to two kilometers down range. Longer ranges are possible by increases in optical performance and emitted laser energy. By exploiting the laser returns from an object and comparing them to high resolution laser baseline information, LPAS is capable of rendering awareness of only objects moving on the ground within a perimeter while ignoring the background clutter. Also, in LPAS, raw laser return data may be used in concert with visible or IR camera images for shape classification and alarm cueing in an integrated and autonomous environment.
With LPAS, it is possible to detect and determine range, bearing and elevation of moving and newly appearing objects and to determine threat potential to a target at which LPAS is located using shape feature classification and well defined constant bearing decreasing range (CBDR) algorithms. However, LPAS can not establish objects that are different than those expected in the naturally occurring or urban environment.
While LOAS, LPAS, and other laser or conventional radar systems provide object detection, they do not provide the real intelligence in order to classify the type of threat which is desirable to aid military forces operating in the wide range of environments. Of particular importance is the ability of an active laser system to detect and classify threats in heavily urban or mountainous environments at short ranges. This is critical today as military forces pursue non-combatants in urban and rural environments. A laser sensing system which will bring to the warfighter a capability to know his or her threat environment long before the enemy can take action will create an overwhelming position of dominance.
The present invention is intended to improve upon the LPAS and provide a laser sensing system capable of detecting and classifying the type of threat which will aid military forces operating in the wide range of environments, especially in heavily urban or mountainous environments. Likewise, it eliminates significant cost, complexity, and weight of passive sensors, such as cameras, infrared sensors, and multi-spectral and hyper-spectral devices.